1. Field of the Invention
This invention relates to a recording apparatus and an ink jet recording method, and particularly to a recording apparatus and a recording method in which recording can be effected in a plurality of resolvability or resolution modes.
2. Related Background Art
With the spread of copying apparatuses, information processing apparatuses such as word processors and computers and further, communication apparatuses such as facsimile apparatuses, apparatuses for effecting digital image recording by an ink jet system have spread as one type of image forming (recording) apparatuses for outputting information processed in those apparatuses as characters and images. In recent years, it has been rapidly contrived to cope with effecting recording of higher resolvability to meet the demand for the higher quality of recorded images.
In such an ink jet recording apparatus, generally with a view to improve the recording speed, a recording head having a plurality of ink discharge ports and liquid paths integrated is used as a recording head comprising a plurality of recording elements integrated and arranged. However, the integration density of the ink discharge ports is limited for a reason in the manufacture or the like and therefore, it is the present situation that the resolvability required in recent years cannot be coped with by the construction of the recording head like that heretofore available. In contrast, there have already been proposed various recording methods for effecting recording of high resolvability by the use of a recording head of relatively low resolvability.
Xerox Disclosure Journal, March/April 1979, vol.4, No. 2 shows a method of forming an image by the recording scanning of a head having nozzles (ink discharge ports) arranged at a pitch .lambda. and paper feeding of n+1/2 .lambda. (n being an integer). This can form an image in which the pixel pitch is 1/2 .lambda., i.e., an image of double resolvability, by the use of a recording head in which the nozzle pitch is .lambda.. That is, what is written clearly in this literature is the most basic technique for obtaining an image of higher resolvability by effecting interlace recording several times by the use of a head of low resolvability.
In contrast with this, U.S. Pat. No. 4,198,642 by Mead Corporation and U.S. Pat. No. 4,920,355 by Eastman Kodak are mentioned as what specifically show the construction as a recording apparatus. According to the former, the nozzle interval is Kp and the number of nozzles is n for the recorded pixel interval q, and K and n are prime integers greater than 1, whereby an image can be recorded having resolvability k times as great as the nozzle pitch by a predetermined amount of paper feeding and the repetition of recording scanning. Also, according to the latter, when recording is effected by the use of A nozzles disposed at 2-pixel pitch, there is clearly written that A is an even number and a method in which an image is formed by the repetition of (A-1) pixels and (A+1) pixels for the amount of paper feeding in each recording scanning cycle, and here is realized resolvability double the nozzle pitch.
These cases are common in that the gap of the recording interval of each nozzle in one recording scanning cycle is made up for by a plurality of cycles of recording scanning and a particular amount of paper feeding, that is, interlace recording is effected, and an image of higher resolvability than the resolvability of the head in use can be realized.
However, when recording of high resolvability is done by the method of each of the above-described examples of the prior art, the time required for the data processing for interlace recording and the time required for the recording itself are apt to become long. Particularly in the case of data such as characters which do not require a high quality of image, time is meaninglessly consumed for the processing and recording thereof. Therefore, it is also known to further provide a low resolvability mode in which recording is effected at the same degree of resolvability as the nozzle pitch attaching importance to throughput, discretely from a high resolvability recording mode which realizes resolvability greater (greater than double) than the nozzle pitch (the pitch of the discharge ports).
Now, in a case where a plurality of resolvability modes are set as described above, when the resolvability is changed by mode changeover, the size of a pixel to be recorded is also changed, but in such a case, from the viewpoint of the dignity of recording or the like, it is desirable that the diameter of a dot can be adjusted in conformity with the size of the pixel. In the case of the ink jet system, however, it is difficult in terms of the structure thereof to change the size of each ink droplet discharged from each discharge port of a recording head within a range conforming to a change in the size of the pixel. Usually, in an ink jet recording apparatus corresponding to predetermined resolvability, the amount of ink discharge is designed in conformity with the predetermined resolvability. For example, when said predetermined resolvability is 360 dpi as shown in FIG. 1A of the accompanying drawings, the size of the dot diameter on the surface of paper is set to such a degree of discharge amount that completely covers a pixel, i.e., an area of 70.5 .mu.m square.
However, if recording of 720 dpi is done with this setting of the discharge amount kept, four dots of the same size as in the case of 360 dpi are formed on the same area as the above-mentioned pixel as shown in FIG. 1B of the accompanying drawings, and the number of recorded dots, i.e., the amount of ink placement, per unit area becomes four times as great as that in the case of 360 dpi. If recording of 720 dpi is thus done when the design of the discharge amount corresponds to 360 dpi, the amount of ink placement will become excessively great and this may cause the deterioration of image in respect of the flow or the like by more ink than necessary. It may also cause the problem that image density and harmony differ greatly depending on resolvability.
In contrast with this, in a prior-art ink jet recording apparatus corresponding to a plurality of resolvability modes, there is adopted a method of setting the discharge amount to a value smaller than a discharge amount suitable for the low resolvability mode and greater than a discharge amount suitable for the high resolvability mode, and recording a plurality of dots for a recording pixel after binarization in the low resolvability mode and regularly thinning (e.g. checkerwise) pixels arranged on the surface of paper in the high resolvability mode to thereby reduce the number of dots formed in unit area. It is known that by doing so, the amount of ink placement is kept substantially constant without resorting to resolvability.
However, there is also a case where depending on the recording medium used, it is inappropriate to change the number of ink droplets uniformly placed into each pixel (the number of dots formed) in conformity with resolvability. For example, there has been a case where sufficient density is not obtained even if a dot or n dots are formed for a pixel and at the same time, the amount of ink placement becomes excessively great to cause the deterioration of image such as the blur of ink when two dots or (n+1) dots are formed for a pixel, and there has also been a case where it is difficult to determine the optimum number of dots for a pixel conforming to resolvability.
Particularly, when a colored image is to be recorded, in addition to the above-described change in the number of dots conforming to resolvability, it is necessary to record dots of two or more colors for a pixel when secondary colors such as red, green and blue are to be recorded, and in such a case, sufficient density is not obtained in a monochromatic image unless two or more dots are recorded for a pixel and on the other hand, the amount of ink placement may sometimes become excessive if for example, two dots are recorded in a mixed-color portion wherein secondary colors are recorded as described above.